The present invention relates to a two-cylinder thick matter pump having a piston storage.
With its piston storage the inventive two-cylinder thick matter pump compensates pressure and volume fluctuations in the feed pipe that arise between the strokes of the cooperating feed cylinders. These fluctuations, that disturb the uniformity factor of the feed, are, for constructional reasons, larger in the case of mechanically controlled feed cylinders, e.g. feed cylinders whose pistons are driven with a crankshaft, than in the case of hydraulically driven feed pistons, which allow the piston strokes to be covered but cannot prevent pressure and volume fluctuations in the feed pipe, either, when the piston of the feeding cylinder is switched over to the suction stroke and the piston of the feed cylinder sucking out of the prefilling vessel of the pump is switched over to the pressure stroke. In this switch-over phase the piston storage presses thick matter into the feed pipe, thereby at least partly compensating the pressure and volume loss of the switch-over phase.
The inventive two-cylinder thick matter pumps thus differ from piston pumps which aim to improve the uniformity factor of the thick matter feed with at least three or even more feed cylinders, because with such pump constructions thick matter must be sucked out of the prefilling vessel with the second or additional feed cylinders, while with the piston storages the additional feed volume passes from the feed pipe into the storage and from there back into the feed pipe during the switch-over phase of the feed cylinders. Thick matter pumps having more than two feed cylinders to compensate volume and pressure fluctuations in order to increase the uniformity factor in the feed pipe can reduce the pressure fluctuations at the expense of a simple mechanical construction and simple control means, with a considerable increase in technical effort, but they cannot avoid speed droops in the feed.
The invention relates in particular to thick matter pumps which feed sludge. This may be turbid coal slime for acting upon furnaces with fossil fuels, sewage sludge, mortar and plaster compounds or the like, but particularly media which tend to solidify in the rest phase of their feed and thus cake on the walls of feed paths that at times conduct no feed stream. Such media are above all hydraulically setting media and sludges with pozzolanic properties. It is often important to feed such substances at a high uniformity factor because pressure and volume fluctuations in following installations, e.g. in furnaces, cause difficulties or led to considerable dynamic stresses, which is the case in particular with high lifts.
To compensate such fluctuations the invention employs a piston storage. Piston storages generally use a cylinder built onto the feed pipe and opening into it on one side while its other end is closed by a movable piston. Such piston storages differ from bubble storages by the piston, and from air domes by the fact that the pumping medium is closed off in the storage by a firm but movable wall. Piston storages permit virtually any feed pressure and can therefore be used together with pumps that reach considerable lifts.
The invention starts with a known thick matter pump that works with a piston storage. The storage piston works with its side facing away from the pumping medium on a pressure cushion consisting of a high-pressure gas. During the pressure stroke of the feed cylinders the storage cylinder fills up with pumping medium from the feed pipe, whereby the storage piston compresses the gas cushion. As soon as the pressure collapses, or drops, in the feed pipe in the switch-over phase, the high-pressure gas cushion urges the piston in the opposite direction and presses pumping medium out of the storage cylinder into the feed pipe. Such a piston storage can in fact improve the uniformity factors of thick matter feed.
However, the disadvantage is that a complete evacuation of the storage cylinder is not ensured. This has various causes, but the consequence is that pumping medium tending to cake or harden prematurely impairs the storage relatively quickly and eventually blocks it. This not only reduces the uniformity factor of the feed but also results in disturbances in the feed which are relatively difficult to eliminate.